ARLINGTON (CBSDFW.COM) – A man was trapped in an old bank vault for three hours on Thursday evening after a practical joke went wrong.

It happened at an Allstate Insurance Office on Randol Mill Road near North Fielder Road in Arlington. It’s unclear exactly how it happened, but one employee was locked inside the vault by a co-worker.

“It was a stupid accident,” said office owner Jeff Hemenz. “The police and fire were called to help get an employee out of the bank vault because it was an old bank vault and we weren’t able to open it.”

Hemenz says the employee had little to do in the empty vault, which measures a couple hundred square feet. He wasn’t present at the time but says everyone involved remained calm as the Police and Fire Departments worked to free the man.

The employee, who was freed around 10:30 p.m., was not injured in the incident.

“I haven’t talked to him this morning yet,” said Hemenz. “I’m kind of letting him sleep in.”